The characterization of a concentration-sensitive α-adrenergic-like octopamine receptor found on insect immune cells and its possible role in mediating stress hormone effects on immune function
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► First molecular demonstration of octopamine receptors in an insect immune cell suggests that the neural-immune connections may be conserved from insects to mammals.
Introduction
The nervous system regulates the immune system in vertebrates (Sternberg, 2006, Tracey, 2009). However, the effects of neurally-derived molecules (e.g. neurohormones) on immune cells, and the importance of these effects on immune system function, are still controversial (Nance and Sanders, 2007). For example, some studies show that norepinephrine, released by the sympathetic nervous system during the stress response, increases immune and pro-inflammatory responses (Garcia et al., 2003, Johnson et al., 2005, Lang et al., 2003, Straub et al., 2000) but other studies find that it causes immunosuppressive effects (Alves et al., 2006, Woiciechowsky et al., 1998). In part these controversies exist because the underlying molecular mechanisms are incompletely understood (Franco et al., 2007, Sternberg, 2006, Tracey, 2009).
Compounds released during the stress response also have complex effects on immune function in invertebrates (Adamo, 2008). Octopamine, the insect equivalent of norepinephrine (Roeder, 1999), enhances phagocytosis by insect immune cells (i.e. hemocytes) (Baines et al., 1992, Baines and Downer, 1994, Kim et al., 2009), but it can also reduce immune function and disease resistance (Adamo and Parsons, 2006, Adamo, 2010). Unfortunately the molecular mechanisms underlying OA-mediated immunoregulation of insect hemocytes are poorly understood, making this apparent contradiction difficult to resolve. OA is thought to induce these effects via octopamine receptors (OARs) located on insect immune cells (Adamo, 2008), although the molecular evidence for their existence on these cells is lacking. In fact, there are no published molecular studies to-date to verify earlier pharmacological work suggesting that receptors for stress hormones are widespread in invertebrate immune cells (Adamo, 2008).
Understanding how octopamine induces complex effects in insect immune cells may shed light on how norepinephrine produces similarly complex effects in vertebrate immune cells. The octopaminergic and noradrenergic systems are thought to have evolved from the same ancestral system because of the molecular similarities between norepinephrine and octopamine, as well as between their receptors and transporters (Evans and Maqueira, 2005). For example, the octopamine receptor is a typical rhodopsin-like G protein-coupled receptor that has a sequence similar to that of vertebrate adrenergic receptors (Evans and Maqueira, 2005). In cells outside of the immune system, the binding of OA to OARs has been shown to activate coupled G-protein effector pathways, thereby inducing the generation of intracellular second messengers such as cAMP and/or Ca2+ (Roeder, 2005). Vertebrate adrenergic receptors are also known to activate multiple second messenger systems in some vertebrate cell types (e.g. Cotecchia et al., 1990), although, as in insects, this issue has not been well studied in immune cells. If insect hemocytes have adrenergic-like receptors, it may be possible to test whether these receptors are capable of mediating complex responses to stress hormones/neuromodulators. This information is likely to be relevant to vertebrate immune cells as well.
In the present study, we provide molecular evidence that hemocytes of the striped stem borer (SSB), Chilo suppressalis (Walker) (Lepdiopter: Crambidae) carry an OA receptor (CsOA1) on their hemocytes. We then demonstrate that these immune cells show complex responses to stress hormone OA. We test whether some of this complexity is mediated via different second messenger systems activated by the OAR.
Section snippets
Insects
The larvae of the striped stem borer (SSB), C. suppressalis were collected from fields in Fuyang (30°3′58.93″N, 119°55′49.95″E), Zhejiang Province, China, in 2010. The collected SSB larvae were reared on an artificial diet (Liu et al., 2008) at 28 °C under a 16:8 L:D photoperiod for several generations prior to experiments.
Hemocyte-spreading assay
The in vitro bioassay was modified from an established method (Clark et al., 1997). Fifth-instar larvae of SSB were surface-sterilized with 70% ethanol. The proleg was cut
OA showed biphasic effects on cellular immune responses
10 nM and 100 nM OA enhanced hemocyte spreading significantly (one-way ANOVA, F(6, 20) = 28.8; 10−8 M, t = 5.0, p = 0.004; 10−7 M, t = 5.1, p = 0.003), but above 10 μM, OA inhibited the spreading behavior of hemocytes (Fig. 1, Fig. 2, Fig. 3, Fig. 4, 10−4 M, t = −4.2, p = 0.02). Similar results were also found in the hemocyte-phagocytosis assay (Fig. 1B), with concentrations of OA up to 10−7 M enhancing phagocytosis (one-way ANOVA, F(6, 20) = 74.5, t = 6.5, p = 0.0003), but higher concentrations (>10−5 M) inhibiting it (10−5
Discussion
The effect of OA on immune function was concentration-dependent. Low concentrations of OA promoted hemocyte spreading and phagocytosis, probably mediated by increasing intracellular calcium levels. However, high concentrations of OA inhibited hemocyte spreading and phagocytosis via the cAMP pathway. Thus, the immunoregulatory effects of OA on immune function might be different, depending on the amount of OA released.
Earlier studies have also found that OA has biphasic effects on immune
Acknowledgments
Financial support for this study was provided by the National High-tech R&D Program of China (2011AA10A204), National Natural Science Foundation of China (31000849), Qianjiang Talent Program of Zhejiang Province (2010R10086) and NSERC (Natural Sciences and Engineering Research Council of Canada).
References (45)
Why should an immune response activate the stress response? Insights from the insects (the cricket Gryllus texensis)
Brain Behav. Immun.
(2010)- et al.
The emergency life-history stage and immunity in the cricket, Gryllus texensis
Anim. Behav.
(2006) - et al.
Cohabitation with a sick cage mate: effects on noradrenaline turnover and neutrophil activity
Neurosci. Res.
(2006) - et al.
Octopamine and 5-hydroxytryptamine enhance the phagocytic and nodule formation activities of cockroach (Periplaneta americana) haemocytes
J. Insect Physiol.
(1992) - et al.
Role of arachidonic acid metabolites in the action of a β adrenergic agonist on human monocyte phagocytosis
Prostag. Leukot Ess. Fatty Acids
(1998) - et al.
Isolation and identification of a plasmatocyte-spreading peptide from the hemolymph of the lepidopteran insect Pseudoplusia includens
J. Biol. Chem.
(1997) - et al.
Multiple second messenger pathways of α-adrenergic receptor subtypes expressed in eukaryotic cells
J. Biol. Chem.
(1990) - et al.
Undertaker, a Drosophila Junctophilin, links Draper-mediated phagocytosis and calcium homeostasis
Cell
(2008) - et al.
Stress-induced changes in the octopamine levels of insect haemolymph
Insect Biochem.
(1984) - et al.
Calcium inhibition and calcium potentiation of Orai1, Orai2, and Orai3 calcium release-activated calcium channels
J. Biol. Chem.
(2007)
Monoaminergic regulation of hemocyte activity
J. Insect Physiol.
Octopamine, a modulator of the haemocytic nodulation response of non-immune Galleria mellonella larvae
J. Insect Physiol.
The emergence of neurotransmitters as immune modulators
Trends Immunol.
A new generation of Ca2+ indicators with greatly improved fluorescence properties
J. Biol. Chem.
Neurotransmitters regulate the migration and cytotoxicity in natural killer cells
Immunol. Lett.
Cyclic AMP affects the haemocyte responses of larval Galleria mellonella to selected antigens
J. Insect Physiol.
Autonomic innervation and regulation of the immune system (1987–2007)
Brain Behav. Immun.
Octopamine in invertebrates
Prog. Neurobiol.
Involvement of both granular cells and plasmatocytes in phagocytic reactions in the greater wax moth, Galleria mellonella
J. Insect Physiol.
The role of octopamine in locusts and other arthropods
J. Insect Physiol.
The cloning, phylogenetic relationship and distribution pattern of two new putative GPCR-type octopamine receptors in the desert locust (Schistocerca gregaria)
J. Insect Physiol.
Parasitic suppression of feeding in the tobacco hornworm, Manduca sexta: parallels with feeding depression after an immune challenge
Arch. Insect Biochem. Physiol.
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